The invention relates generally to a photomask and, more particularly, to a method for correcting a critical dimension of a mask pattern.
A photomask acts to transfers a pattern including an light shielding layer or a phase shift layer on a substrate to a wafer to form a desired pattern. A binary mask has been used as a photomask, in which an light shielding layer is formed on a substrate and then is etched to a desired pattern so that light can be transferred onto the wafer by passing through the substrate alone. However, as the degree of integration of semiconductor devices has increased, a mask capable of forming a finer pattern on the wafer as compared to the binary mask is required. Accordingly, a phase shift mask capable of finer pattern on the wafer using a phase shift material having a transmittance of several percent has been suggested and used. However, it is difficult to accurately realize a target critical dimension (CD) as the CD of a pattern formed on the mask has decreased with decreases of the design rule according to the high degree of integration of semiconductor devices.
Therefore, to more accurately realize the target CD, in the process of fabricating the phase shift mask, a phase shift layer and an light shielding layer are formed on a wafer and then a first patterning process is performed to form an light shielding layer pattern on a main cell region and a frame region. Subsequently, a difference between a CD of the light shielding layer pattern and the target CD is measured. Next, the CD of the light shielding layer pattern is corrected by a correction amount of the measured CD. However, due to the CD correction process, the process steps become complex as a resist layer pattern is formed on the light shielding layer pattern by forming and patterning the resist layer on the substrate and then the light shielding layer pattern is etched using the resist layer pattern as an etch mask. Also, the occurrence of defects increases as the resist layer is applied in the CD correction process, and problems may occur, such as the formation of bridge defects by which patterns are undesirably interconnected. Also, it is difficult to control organic defects such as residues on the resist layer. Thus, while it is possible to realize the target CD by the CD correction process, the mask should be discarded due to generation of uncontrollable defects. Therefore, a method capable of correcting the pattern CD as well as improving the cause generating the defect is needed.